Electrical resistor



Jan. 14, 1930. BRADLEY- 1,743,705

ELECTRICAL RESISTOR Filed Jan. 22, 1925 Patented Jan. 14, 1930 time UNETEQ STATES PATENT OFEEQE LYNDE BRADLEY, OF MILWAUKEE, WISCONSIN, ASSIGHOR TO THE RELIANCE COM- PANY, OF MILW'AUKEE, WISCONSIN, A CORPORATION OF WISCONSIN ELECTRICAL RESISTOR Application filed January 22, 1925. Serial No. 4,050.

This invention relates to certain new and useful improvements in electrical resistors more particularly designed for use in the microphone circuits of radio broadcasting stations.

In broadcasting grand opera or any programme where the artists change their positions during the performance, it is desirable to incorporate a rheostat in the microphone circuit which is operated to increase the resistance in the microphone circuit as the "artist nears the microphone and to decrease the resistance as the artist moves from the microphone. Heretofore, considerable difficulty has been experienced in that the adjustment of the rheostat produces a characteristic click which is broadcast by the station. This is true with a wire-round rheostat, as the contact finger in passing from one coil or turn to another produces a characteristic clickin and with a compressible resistor the engagement of the microscopic irregularities of the adjacent faces of the discs produces a noise in the circuit which is also broadcast.

Having the above and other objectionable features of the attempts heretofore made to vary the resistance in a microphone circuit in mind, this invention has as one of its objects the provision of an improved rheostat which may be readily adjusted without producing any extraneous noises in the circuit,

This invention has as another object the provision of an improved disc for a compressible resistor which will increase the efficiency of the resistor and eleminate the production of any noise incidental to the varying of the pressure thereon.

It is a further object of this invention to generally increase the efliciency of electrical resistors of the character described.

With the above and other objects in view which will appear as the description proceeds, my invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the herein disclosed invention may be made as come within the scope of the claim,

In the accompanying drawing, 1 have illustrated one complete example of the physical embodiment of my invention constructed accrease the resistance in the circuit of the microphone being cut out and decrease the resistance in the other microphone circuit. This system of switching fro-m one microphone to another eliminates the sharp click incidental to the sudden making and breaking of the microphone circuits.

The employment of means for varying the resistance in the microphone circuit is also desirable to permit better control of the microphone in that the resistance is in O creased as the artist or artists near the microphone and is decreased as the artist or artists move from the microphone.

lVhile the adjustment of the microphone circuit during the period of broadcasting is very desirable, it has not been done in the past, except under extraordinary conditions, due to the abjectionable noises created by making such adjustments. lVhen wire wound rheostats are employed, the noise is created by the contact finger slipping from one coil or turn to another. This objection also is true when rheostats of the compressible type are employed as the discs thereof, when viewed under a microscope, have minnute serrations on their faces that engage as pressure is applied producing an objectionable sound which is broadcast.

Furthermore it has been found that when a compressible type rheostat is accidentally tapped or shaken, the rubbing or sliding together of the discs creates an objectionable disturbance or sound in the carrying wave of the broadcasting station, which must be eliminated to insure satisfactory reception.

In the accompanying drawing, I have illustrated an improved rheostat, in which all sounds incidental to its operation have been eliminated, and to which reference is now made.

The numeral 5 designates a panel board or other support preferably of insulating material such as a phenolic condensation product, rubber or the like and provided with an aperture 6 in which the threaded sleeve 7 of the rheostat 8 is secured to firmly mount the rheostat on the panel. The rheostat includes a body number 9 of insulating material such as porcelain or the like provided with two parallel openings or compartments 10 closed at their ends by plates or cover members 11 and 12 suitably secured to the body member.

The inner end of the sleeve 7 is secured to the member 11 in a suitable man er and said member is firmly held against the inner face of the panel board by a locl: nut 13 threaded on the sleeve. The member 12 preferably has an insulating member 1 1 confined between it and the body mem er 9 to insulate the contact members 15 positioned in the openings 10 therefrom. The contact members 15 have extensions 16 which project outwardly of the openings 10 to provide terminals 17 for electrical connection with the conductors of the micropone circuit in which the rheostat is to be included.

Mounted in each chamber 10 with its outermost disc 18 in intimate contact with the adjacent contact member 15 are a plurality of discs 18' forming resistance elements. The resistance elements. are adapted to be bridged by a contact member 19 which is normally urged from engagement therewith by a spring member 20. The member 19 is moved to electrically bridge and compress the resistance elements against spring 20 by a pressure applying screw 21 threaded in the sleeve 17 and having an operating knob 22 on its outer end. the screw 20 is turned into the sleeve 7 the bridging contactor is engaged with the resistance elements gradually applying pressure thereto to decrease the resistance in the circuit in which it is incorporated.

To the naked eye, the surfaces of the discs 18 and 18 appear comparatively smooth, although under microscopic examination they are found to be very rough, having numerous serrations or ribs 23, as shown in the enlarged fragmentary view of two adjacent discs in Figure 2. These irregularities engage as pressure is applied to the resistor elements producing objectionable sounds in the microphone circuit that are As will be evident, as

weaves broadcast, as previously stated. Furthermore a tapping of the rheostat causes the discs to rub and the noise thereof is broadcast.

I eliminate these objectionable sounds by applying a quieting means to the rheostat, which, in the present embodiment, is illustrated as a lubricating iilm 24 covering the surfaces of the discs 18 and 18. The lubricant 24 eliminates all sounds and noises incidental to the engagement or sliding together of the irregularities of the discs, thus permitting the adjustment of the resistance in the microphone circuit without producing any extraneous sounds therein.

Various types of lubricant may be employed and it may be applied to the discs in various ways, such as dipping the discs in a liquid, rubbing the lubricant or quietin means on the discs, or by incorporating a quieting medium in the composition of the discs. Practice has demonstrated that the quieting means may be in the form of a high temperature grease preferably applied to the surfaces of the discs in a thin film altho this is not essential and the grease or other quieting means may be combined with other ingredients in order to give it a degree of conductivity. One of the combinations may be grease or other lubricant mixed with lamp black and graphite, or either of them.

While the drawing illustrates the applicaion of this invention to a rheostat of the compressible type, it is to be understood that the principles thereof may be applied in various types of rheostats.

hat I claim as my invention is:

A compressible resistor for use in a microphone circuit, comprising a supporting member, a resistance element in the sup porting member and including a plurality of stacked discs, there being an air space surrounding the resistor element, means for applying a pressure to the element to vary the resistance offered thereby to the passage of current therethrough, and a film of material covering the contacting surfaces of the resistance element discs, said material having the ability of easing the sliding engagement between irregularities in the faces of adjacent discs as the pressure on the element is adjusted, whereby the microphonic value of the resistance element is rendered substantially nil.

In testimony whereof I affix my signature.

LYNDE BRADLEY. 

